Improved astrometry for the Bohannan & Epps catalogue

Aims: Accurate astrometry is required to reliably cross-match 20th-century catalogues against 21st-century surveys. The present work aims to provide such astrometry for the 625 entries of the Bohannan & Epps (BE74) catalogue of H$\alpha$ emission-line stars. Methods: BE74 targets have been individually identified in digital images and, in most cases, unambiguously matched to entries in the UCAC4 astrometric catalogue. Results: Sub-arcsecond astrometry is now available for almost all BE74 stars. Several identification errors in the literature illustrate the perils of relying solely on positional coincidences using poorer-quality astrometry.Comment: 3 pages, 1 figure. Accepted in A&

The Gaia Astrometric Survey

In its all-sky survey, the ESA global astrometry mission Gaia will perform high-precision astrometry and photometry for 1 billion stars down to $V = 20$ mag. The data collected in the Gaia catalogue, to be published by the end of the next decade, will likely revolutionize our understanding of many aspects of stellar and Galactic astrophysics. One of the relevant areas in which the Gaia observations will have great impact is the astrophysics of planetary systems. This summary focuses on a) the complex technical problems related to and challenges inherent in correctly modelling the signals of planetary systems present in measurements collected with a space-borne observatory poised to carry out precision astrometry at the micro-arcsecond ($\mu$as) level, and b) on the potential of Gaia $\mu$as astrometry for important contributions to the astrophysics of planetary systems.Comment: 2 pages. Summary of an invited talk given at Special Session 6 (Planetary Systems as Potential Sites for Life) of the XXVIIth IAU General Assembly held in Rio de Janeiro (Brazil). To appear in IAU Highlights of Astronomy 15 (2010